A 1 kg block on a spring is modeled by the following initial value problem. x"+4x= 12 cos(4t), x(0) = 0, x'(0) = 0 a) Find the position of the block at time t x(t) = b) Assuming the forcing function and the spring stay the same, what mass would the block have to have for the system to be in resonance? kg. (exact answer)